Packaged systems incorporating multiple die are receiving growing interest. Multi-die packages use synchronous die-to-die links to enable high-speed and low-latency communication between die. A die-to-die link must typically support very large aggregate data bandwidth and favors a parallel bus architecture with a forwarded clock for simpler data retiming at the receiver.
Multi-die systems integrated into single packages are increasingly attractive given recent advances in wafer-level package (WLP) technologies. To make such systems cost-effective, Known Good Die (KGDs) are identified at wafer-level test prior to multi-die integration.
One type of test used to identify KGDs includes a loopback test. In a conventional loopback test, a transmitter (TX) on a die sends a test pattern of binary data, which is received by a receiver (RX) on the same die. Thus, the test pattern is sent from a TX to an RX on the same die, or looped back. The received test pattern is then checked for correctness. If the received test pattern is incorrect, that is an indication that the die being tested may not be a good die.
With functional partitioning of a system into several die, the IO (input/output) communication bandwidth requirement between any two die in one direction is not necessarily the same in the reverse direction. This asymmetric bandwidth requirement complicates the hardware requirements to facilitate wafer-level IO loopback testing. There is thus a need in the art for improved loopback testing.